Polymethylferrocene-Induced Photopolymerization of Cyanoacrylates Using Visible and Near-Infrared Light

Abstract

Metallocene-induced photopolymerization of cyanoacrylates based on electron transfer processes has been proposed as an alternative to more conventional light-curing strategies relying on photobase generators. However, successful application of this methodology has so far only been achieved for very reactive cyanoacrylates under UV illumination and long irradiation times, which eventually hampers its practical use. To overcome these limitations, we describe in this work the use of electron-rich polymethylferrocenes as photoinitiators, with which fast light-induced polymerization of commercial formulations of less reactive, but more relevant long alkyl chain cyanoacrylates has been accomplished by illumination with visible and even near-infrared light. In addition, generalization of this technology to other electron-deficient, noncyanoacrylate monomers has been demonstrated. The low oxidation potential of polymethylferrocenes accounts for these excellent results, which strongly favors the formation of radical anions by electron transfer that initiate the polymerization reaction. Because of the high molecular weight and superior adhesive behavior of the resulting polymer materials as well as the facile access to polymethylferrocenes, they emerge as very attractive photoinitiators for the light-curing of cyanoacrylate (and other) glues in real applications.

Recent advances on ferrocene-based photoinitiating systems

“…[216][217] To overcome this drawback, in 2019, this topic was revisited with the development of electron-rich ferrocenes (See Figure 6). [218] Interestingly, the authors demonstrated the possibility to apply this strategy to the polymerization of two cyanoacrylate monomers of interest, namely butyl 2-cyanoacrylate and 2-octyl 2-cyanoacrylate. Indeed, these two monomers can be found in numerous commercial formulations due to their low toxicities and their high viscosities [219].…”

“…Using these conditions, the polymerization of diEtMM could be ended at 431 s, upon irradiation at 420 nm (I = 46 mW/cm²) (See Figure 8). Reproduced with permission from Faggi et al [218]. Copyright 2019 American Chemical Society.…”

“…Figure 8. Polymerization of diEtMM using Me10-Fc as the photoinitiator (C= 30 mM).Reproduced with permission from Faggi et al[218]. Copyright 2019 American Chemical Society.…”

Recent advances on iron-based photoinitiators of polymerization

“…Recently, photobase generation with ferrocene was revisited in the context of electron-enriched ferrocenes, enabling the polymerization of cyanoacrylates bearing long alkyl chains (See Figure 26). [138] Figure 26. Chemical structures of polymethylferrocenes.…”

“…UV-visible absorption spectra of Me10-Fc in acetonitrile and ethyl 2cyanoacrylate. Adapted with permission from Faggi et al [138]. Copyright 2019 American Chemical Society.…”